Even before Viking 1 landed on Mars (July 20, 1976), NASA and its contractors studied post-Viking robotic Mars missions. Prominent among these was Mars Sample Return (MSR), considered by many to be the most scientifically significant robotic Mars mission. The Viking missions reinforced this view of MSR, and also revealed the perils of making assumptions when planning costly and complex Mars exploration missions. The centerpiece of the $1-billion Viking mission, a package of three biology experiments, yielded more questions than answers. Most scientists interpreted their data as evidence of previously unsuspected reactive soil chemistry, not biology.With that unsatisfying experience in mind, A. G. W. Cameron, chair of the National Academy of Science Space Science Board, wrote in a November 23, 1976 letter to NASA Administrator James Fletcher that[to] better define the nature and state of Martian materials for intelligent selection for sample return, it is essential that precursor investigations explore the diversity of Martian terrains that are apparent on both global and local scales. To this end, measurements at single points. . . should be carried out as well as intensive local investigations of areas 10-100 [kilometers] in extent.Soon after Cameron wrote his letter, NASA Headquarters asked the Jet Propulsion ...

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